1. Field of the Invention
The present invention relates to a rotary electric machine for a vehicle mounted in a car, a truck, and the like.
2. Description of the Related Art
An rotary electric machine for a vehicle is known, in which the output voltage of an armature winding is rectified using an inverter circuit having a plurality of switching elements (refer to, for example, Japanese Patent No. 4023353. In the rotary electric machine for a vehicle, the timing at which the switching element of a certain phase is turned OFF is set to a point at which a delay time based on rotation frequency has elapsed from a point at which the phase voltage of another phase has reached a predetermined threshold value. The rotation frequency used in control such as that described above is detected based on the amount of time between points at which the alternating-side main electrode voltages of the upper arm elements of two adjacent phases exceed a predetermined threshold value (the time difference between points at which the voltages of two phase windings exceed a predetermined threshold value).
In a vehicle power generator disclosed in Japanese Patent No. 4023353, when power generation voltage changes in accompaniment with fluctuations in electrical load and the like, the point at which the phase voltage exceeds the predetermined threshold value shifts. Therefore, a problem occurs in that the accuracy of rotation frequency detection decreases with the change in power generation voltage. For example, the power generation voltage increases when the electrical load is suddenly reduced. Therefore, the point at which the phase voltage exceeds the predetermined threshold value becomes slightly earlier. Thus, the amount of time between the two points at which rotation frequency detection is performed becomes shorter compared to when the power generation voltage is constant. A judgment that the rotation frequency has increased is erroneously made.